The invention relates to hinge joints in general, and more particularly to improvements in hinge joints which can be utilized with advantages to establish pivotable connections between the body supporting portions and the back rests of seats, especially of seats in motor vehicles.
It is well known to pivotally connect the back rest to the body supporting portion of the driver's seat or another seat in a motor vehicle by a hinge joint wherein a first component or leaf is rigidly connected with (or forms an integral part of) the body supporting portion, a second component or leaf is rigidly connected with (or forms an integral part of) the back rest, and a coupling member in the form of a pintle forms an element of the means for adjustably connecting the two components to each other so that the second component can be pivoted to any one of a number of different angular positions and can be releasably locked in a selected angular position with reference to the first component. The connecting means can further comprise a set of mating gears and/or other suitable means for releasably holding the second component in the selected angular position with reference to the first component and the body supporting portion of the seat. It is further known to provide the coupling member with a frustoconical eccentric portion which is biased axially of the coupling member by a suitable spring and serves to move one element of the holding means radially of another element prior and/or during adjustment of inclination of the back rest. The frustoconical eccentric portion is received in a complementary frustoconical hole or bore of one of the components. Reference may be had, for example, to European Pat. No. 48 294 which further discloses that the eccentric portion of the coupling member is adjustable to permit a change of inclination of the back rest with a minimum of effort. Such adjustability is possible because the shaft which carries the eccentric portion is free to yield in the axial direction when the static friction between the eccentric portion and the adjacent surface is converted into sliding friction at the onset of an adjusting operation. The shaft further comprises a first coaxial (non-eccentric) portion which is journalled in the other component of the hinge joint, and such other component has a bearing sleeve which surrounds a part of the one component around the eccentric portion of the coupling member. A second concentric or coaxial portion of the coupling member is also rotatably journalled in the sleeve, and the two coaxial portions of the coupling member flank the frustoconical eccentric portion. Dual journalling of the sleeve is necessary in order to ensure that the axis of the eccentric portion will remain parallel to the pivot axis for the second component of the patented hinge joint. Such design of the hinge joint is quite satisfactory; however, the bulk of the hinge joint in the axial direction of the coupling member is excessive, primarily because the two coaxial portions of the coupling member must be journalled in the other component of the hinge joint and such coaxial portions must be disposed at opposite axial ends of the frustoconical eccentric portion. It is desirable to keep the dimensions of the hinge joint to a minimum, especially if the hinge joint is used in the seat of a motor vehicle wherein the space is at a premium and wherein the back rest is normally mounted on two spaced-apart hinge joints. The axial length of the aforementioned bearing sleeve at least matches the combined axial length of the two coaxial portions and the frustoconical eccentric portion of the coupling member.